Aristolochic acid binds covalently to the exocyclic amino group of purine nucleotides in DNA.
The plant extract aristolochic acid (AA) has been used as a herbal drug in many cultures since antiquity. In 1982 AA was shown to be mutagenic and a strong carcinogen in Wistar rats. The crude mixture consists of five nitrophenanthrene carboxylic acid derivatives with aristolochic acid I [AA I; 8-methoxy-6-nitro-phenanthro-(3,4-d)-1,3-dioxolo-5-carboxyli c acid] being the major component. The isolated compound has been found to be mutagenic in the Ames assay. The major metabolite of AA I formed under anaerobic conditions in vitro and excreted in vivo in several species including man, is the reduction product aristolactam I. Using the 32P-postlabeling assay, we could show that AA I forms covalent DNA adducts upon metabolic activation in vitro and in vivo in different organs in the rat. Xanthine oxidase, a mammalian nitroreductase, has served as a sufficient model system mimicking the reductive route of in vivo activation of carcinogenic nitroarenes. This paper reports on two major fluorescent adducts of AA I formed by in vitro reaction of AA I with xanthine oxidase and deoxyguanosine or deoxyadenosine. After isolation and purification by preparative HPLC the adducts were characterized by 1H-NMR, FAB mass, UV/Vis and fluorescence spectroscopy. Their structures were elucidated as 7-(deoxyguanosin-N2-yl)-aristolactam I and 7-(deoxyadenosin-N6-yl)-aristolactam I. These findings are in marked contrast to the results reported for other nitroaromatic carcinogens, where C8-modified deoxyguanosine adducts predominate and N2-substituted deoxyguanosine derivatives are found as minor reaction products. Our results suggest a cyclic N-acylnitrenium ion with delocalized positive charge as the ultimate carcinogenic species, binding preferentially to the exocyclic amino group of purine nucleotides in DNA.
Pfau
W
W
Institute of Toxicology and Chemotherapy, German Cancer Research Center, Heidelberg.
Schmeiser
H H
HH
Wiessler
M
M
D034341:Aristolochic Acids; D002273:Carcinogens / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D009153:Mutagens / Q000378:metabolism*; D010616:Phenanthrenes / Q000378:metabolism*; D011685:Purine Nucleotides / Q000378:metabolism*
D034341:Aristolochic Acids; D002273:Carcinogens; D009153:Mutagens; D010616:Phenanthrenes; D011685:Purine Nucleotides; D004247:DNA; C000228:aristolochic acid I